The communication route between communicating devices can include a signal that is transmitted from a first device and received at another device, and another signal that is transmitted from a second device and received at the first device at the same time that the first signal is transmitted. To avoid interference between the two signals, duplex communication networks may be employed. Generally, duplex communication networks allow users to communicate in parallel with one another using schemes such as Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA).
TDMA uses time-division multiplexing to separate incoming (received) and outgoing (transmitted) signals. Because the incoming and outgoing signals are separated in time, the signals may be carried on the same frequency.
FDMA uses transmitters and receivers that operate on different frequencies. The frequencies of the transmitted and received signals can be sufficiently separated such that their modulated frequency spectra do not overlap.
Nevertheless, there are disadvantages associated with the schemes mentioned above. For example, the efficiency of time-division multiplexing is reduced because of the need to coordinate sending and receiving, and delivery of signals may be delayed because of the need to separate the signals in time. Frequency-division multiplexing can be problematic because of the relative scarcity of frequency spectra and the growing number of users and applications.
Full Duplex (FD) operation, also known as Division Free Duplexing (DFD), is a promising alternative to the above schemes. FD or DFD devices transmit in the same time slot and at the same frequency as other devices. As a result, a wireless transceiver device may be transmitting and receiving signals at the same time and at the same frequency. Thus, a key challenge to FD or DFD operation is how to address self interference (interference between the signals transmitted by and the signals received by the transceiver device). More specifically, the transmit power ratio may be larger than zero dBm while the receive power ratio may be less than −90 dBm, a difference of a factor of more than one billion. Therefore, a key challenge to FD or DFD operation is how to address interference of a signal being transmitted on a signal at the same frequency that is being received at the same time.